Mixture control



NOV 20, 1945- I R. K. THOMPSON ErAL 2,389,219'

`MIXTURE CONTRGL Filed Oct. 18, v1943 Il e i E Eizo): '.Roezi If. Tampsap INVENTOR.r

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Patented Nov. 20, 1945 MIXTURE CONTROL Robert K. Thompson and Keith E. Dixon, Detroit, Mich., assignors to George M. Holley and Earl Holley Application October 18, 1943, Serial No. 506,764

1 Claim.

The object of this invention is to control the mixture ratio in a variable Venturi carburetor so that the mixture ratio is maintained at the desired value when the throttles are opened and closed, when the altitude varies and when the airilow varies independently of altitude and throttle position. The figure shows diagrammatically the p preferred form of our invention.

In the drawing, the air entrance I supplies air to a mixture outlet II controlled by a pair of throttles I2 and I3, which, between them, form a variable venturi. These throttles are connected by gears I4 and I5, which gears I4 and I5 are driven by the gear I6 which is rotated by the driveshaft II on which is mounted the cam I8. 'Ihis cam I8 engages with the roller I9 and thus moves the needle as the throttles are opened.

The fuel enters through a passage 2|, flows through a diaphragm chamber 50, formed by the diaphragms 5I and 52, along passage 23 through an orifice 24 which is controlled by the valve 2li. -The fuel then descends in passage 25 and escapes through the openings 26 and 2l into the throat of the variable venturi, formed by the two throttles I2 and I3. The average value of the pressure in the air entrance is obtained at the number of openings 28 and 29 which communicate with a channel 30. This channel 30 communicates through a restricted opening 3| with passage 25, which passage provides air for atomizing the fuel in passage 25. This passage .25 communicates through an opening 32 with a chamber 33 which is separated from an atmospheric chamber 34 by a diaphragm 35. This diaphragm 35 is subjected to the pressure in the air entrance l0 through the'openings 36 and 38. The opening 31 insures a circulation of air in the chamber 34 in which is located the partially evacuated barometric elements 39. This element is thus adapted to respond to changes in atmospheric pressure and changes in temperature. A needle4li is moved by the diaphragm 35. The upper part of needle 40 is hollow and the lower portion has a negative taper which controls the opening 4 I. As the valve 40 is hollow and is notched at its upper end, it provides an unrestricted communicating passage from the orice 4I to the chamber 33. This opening 4I communicates with a passage 42 and thus with the chamber 43 which is connected to the chamber 44. These air chambers are located to the right and left-hand sides of the diaphragms constituting the diaphragm chamber 22 and thus these air chambers control the pressure under which the fuel flows in passage 23 in a well known Passage 42 communicateswith the channel 30 through a restriction 45. The diaphragm is supported by the spring 46 and a smaller spring 41 which holds the needle valve 40 pressed against the diaphragm. 35. This is to prevent the needle from binding in its guide. A compression spring 48 separates the barometric element 39 from the diaphragm 35 and opposes the two springs, 46 and 41. In order that the level in the diaphragm chamber may be as high as possible without flooding, a spring 49 may be used to adjust the level when the engine is not running.

Operation l When the throttles are open in the position shown by means of an anti-clockwise rotation of the shaft Il, the increased airflow through the variable venturi causes fuel to ow past the restriction 24. The quantity of fuel flowing is determined by the cam I8 which determines the opening between the needle 2D and the restricted orifice 24. 'I'here is thus a mechanical connection between the opening of the air passage and the opening of the fuel passage. Such an arrangement would be satisfactory on a marine engine where every position of the throttle corresponds to a definite number of revolutions per minute of the engine. Obviously, in an airplane with a variable pitch propeller We can change the load and the altitude so we therefore have to correct for varying loads and varying altitudes. It is also desirable to correct for varying temperatures as an increase of temperature decreases the density of the air just as an increase in altitude. Hence the valve 40 responds to the increases and decreases in temperature and pressure. This varies the opening through the orifice 4I and therefore more or less of the suction in the passage 25 is transmitted to the chambers 43 and 44 through the hollow needle 40. The variation in load which occurs when the pitch of the propeller is changed is transmitted to the diaphragm 35 which responds to the difference of pressure between the air entrance and in the throat of the venturi. The needle 40 therefore responds to variations in both load and altitude.

We have found that it is possible to correct and to maintain the mixture within fthe desired limits by means of the shape of the needle 40. The orice 45, when the orifice 4I is closed by the needle 4U, is able to subject chambers 43 and 44 to atmospheric pressure or pressures substantially equal thereto. The barometric element 39 responds to changes in the atmospheric pressure, the diaphragm' 35 responds to changes in the drop in pressure in the throat of the venturi, and these two elements I8 and 35 are coupled together so as to vary the position of the valve 40 in the orifice il. The relative area of the variable orifice Il to the fixed orice 45 determines the pressure in the chambers 43/46.

What we claim is:

A variable Venturi carburetor, an air entrance. a fuel entrance adapted to discharge into the throat of said variable venturi, a fuel supply chamber having a moving wall, an air chamber associated with said moving wall, an air pressure regulating chamber, a diaphragm therein dividing said air pressure regulating chamber into an atmospheric chamber connected to the air entrance and a sub-atmospheric chamber connected to the throat of said variable venturi. barometric means located in said atmospheric chamber spring means interposed between said diaphragm and said barometric means, a passage connecting said sub-atmospheric chamber with the first-mentioned air chamber. a restricted air entrance into said passage. valve means operatively connected to said diaphragm, spring and barometric means and adapted to control the connection of said passage 'with said sub-atmospheric chamber.

ROBERT K. THOMPSON; KEITH E. DIXON. 

